Residents of Taiwans
capital may be worried about the 101-story building rising
in their typhoon- and earthquake-prone city, especially in
this era of heightened fears of terrorism. However, Taipeis
508-meter-tall tower, destined to grab the record from Kuala
Lumpurs twin Petronas Towers when it opens late next
year, is the safest place in town, says its structural designer.

"If this building is going
to be damaged, other buildings in Taipei will collapse,"
claims Shaw Shieh, president of the towers local structural
designer, Evergreen Consulting Engineering Inc.

Taipei 101s steel megacolumns
are designed to keep the $700-million skyscraper standing
tall under extreme conditions. But their erection has been
a humbling experience, helping to delay completion by a year.
"Welding was one of the most difficult aspects,"
says Dugald MacKay, project director with Turner International,
New York City, the project manager.

A March 31, 2002, earthquake was
equally disruptive. In that incident, two cranes toppled,
killing five workers (ENR 4/8/02 p.14).

Taipeis 200,000-sq-m tower
rises from a roughly 53-m-square footprint. The four exterior
walls of the lower 25 stories slope inward nearly 5°.
Above that, eight stacked, dimensionally identical modules,
each eight stories and with 7° outward-leaning facades,
rise to level 90. Topping that are 11 mechanical equipment
levels that step back three times. A 60-m-tall pinnacle, rising
from the 101st story, completes the tower at 508 m. Two dampers
within the pinnacle and another suspended from the 92nd level
reduce wind vibrations (see p. 28). A linked, five-story podium
at the base contains a shopping mall, which is now open.

Each module is isolated by smoke
and fire barriers, and contains independent security systems.
Fire- and smoke-resistant safety stairways and corridors also
provide security.

Over a day and a half last month,
workers using strand jacks lifted the 470-tonne pinnacle to
its full height from within the structure, where it had been
partially built. The lift made the tower 56 m taller than
Malaysias twin Petronas towers. However, "it was
never the original idea to build the tallest building,"
says Hong-Ming Lin, president of owner Taipei Financial Center
Corp.

Early plans called for a 60-story
tower with a pair of 20-story blocks, one for each of two
anchor tenants, says Lin. But because both tenants wanted
space in the main block, the developer proposed a single 88-story
tower.

"My partner C.Y. and I have
always wanted to build something very tall," says C.P.
Wang, C.Y. Lees vice chairman. "With the encouragement
of the mayor...we [then] convinced the owner to go higher."

That decision six years ago led
to trouble. After local approvals for 101 stories had been
secured, the height was challenged by the local airport operator,
recalls Shieh.

While waiting for that to be resolved,
engineers sized the structure to accommodate the heaviest
seismic and wind loads for 88 and 101 stories. The process
avoided revisions later on but was one of the earliest causes
of delay, says MacKay.

In selecting a structural system,
Evergreen was inspired to adopt the "megacolumn"
concept of Chicagos unbuilt 610-m-tall Miglin Beitler
tower, designed by New York City-based Thornton-Tomasetti/Engineers.
T-T joined the Taipei 101 team in 1998. Shieh says he welcomed
the firms involvement. "They made us feel more
confident about designing a supertall building," he says.

To provide the biggest lever arm
against overturning, the structure concentrates main loads
in two, generally 3 x 2.4-m vertical megacolumns, 22.5 m apart
along each face, almost touching the sloping perimeter wall
at its base. Main floor girders connect each megacolumn through
moment connections with a core corner column along the same
gridline, forming a tick-tack-toe board (see drawing, p. 26).
The 22.5-m-square core comprises 16 box columns in four lines,
which are generally fully braced between floors. Composite
floors are typically 13.5 cm thick.

At equipment floors every eighth
level, outriggers connect megacolumns and the core. Outriggers
are generally formed by vertically bracing main floor girders
above and below equipment floors. Further crossbracing between
main perimeter columns at these levels forms belt trusses
around the tower. Two minor outriggers connect the cores
central columns with sloping H-shaped uprights in each modules
face.

From just below level 26 down,
megacolumns slope with the buildings profile. Two, 2
x 1.2-m columns are added toward the center of each facade,
while each corner is supported by an additional 1.4-m-square
sloping box column.

Corner columns are tied to the
main frame with two-story-deep belt trusses under levels 9,
19 and 27. All other sloping megacolumns are connected to
core columns with double-story outriggers at these levels.

Designed for axial loads up to
38,000 tonnes, main megacolumns are made of steel as thick
as 8 cm. Along with the core elements, megacolumns are filled
with 10,000-psi reinforced concrete up to level 62. Additional
box columns below floor 26 are also filled.

For enhanced resistance to seismic
forces, main girders and the facade framework have welded
connections to the megacolumns. For additional ductility,
key main beams have reduced flange widths next to column welds.

The design criteria are tougher
than needed to comply with local codes, says Shieh. Codes
require the frame to stay elastic in a 100-year shock and
remain upright through a 950-year event. But actual capabilities
are better, claims Shieh. The building is engineered to stay
up under a 2,500-year shock, corresponding to 0.5-g ground
acceleration.

For fast-track construction, the
owner awarded a 41-month general contract for the tower and
podium base buildings, worth roughly $590 million, to the
KTRT joint venture in June 1999. Divisions of Tokyo-based
Kumagai Gumi Co. Ltd. control KTRT, with the rest divided
among RSEA Engineering Corp. and another firm, both local.

Tower construction got off to a
rough start in late 1998, with a German subcontractor struggling
to pile through clay-rich soil to bedrock 40 to 60 m below.
With equipment designed for stiffer material, pile verticality
was "way over the limit," says Shieh. A local contractor
took over to complete some 380, 1.5-m-dia tower piles. A foundation
slab, 3 m deep at the edges, covers the piles, thickening
to nearly 5 m under megacolumns.

A joint venture of Tokyo-based
Nippon Steel Corp. and Taiwanese China Steel Structure Co.
Ltd., Kaoshiung, began column erection in June 2000 and topped
out in July (ENR 7/14 p. 14). Crews are completing final structural
elements under the pinnacle as part of a $105-million fabrication-erection
contract for 106,000 tonnes of tower and podium steel.

Of over 90,000 tonnes of tower
steel, about 80% is grade 60, which is 25% stronger than the
standard product, says Yoshitaka Ushio, the joint ventures
project director. The steel was made using the thermomechanical
control process for lower carbon and higher weldability.

But ensuring high-quality, full-penetration
welds of such thick plate in site conditions with fabrication
inaccuracies was a struggle, says Hideo Aogaki, KTRTs
project manager. Welding was "critical to progress"
and a significant cause of delay, he adds.

Design changes, especially relating
to the shopping mall, "from beginning to end" caused
delays, says Aogaki. "It wasnt just a simple matter
of changing pipe runs. Shop drawings for the steel had to
be revised and fabrication had to be altered," says MacKay.

Erecting
and welding steel columns was major challenge. (Photo
courtesy of Turner International)

With design changes allegedly causing
delays, increasing steel weight by 10% and raising welding
materials quantities, Ushio believes his joint venture has
earned around $30 million above the contract, not including
the full impact of the crane collapses, where two of four
luffing cranes supported on the 49th floor broke up under
the shock. The building, which was not damaged directly by
the quake, suffered from the falling debris, with parts of
one crane puncturing the podiums roof.

The cranes had complied with local
regulations, later deemed "deficient," says MacKay.
Crane regulations throughout Taiwan have been changed to require
increased seismic resistance, he adds.

The earthquake damaged three of
four cranes used primarily for steel erection. The fourth,
which could operate at reduced capacity, helped install three
new ones. It was then replaced for it no longer complied with
the new regulations. Two cranes had been specially made in
Australia with a 100-tonne capacity at a 22-m radius. It took
nearly four months to get replacements.

An official accident investigation
has yet to issue its report. The owner, general contractor
and steel team continue negotiating over responsibility for
associated delays. Insurance covered the physical damage,
including more than 500 tonnes of new steel for the podium
roof and minor repairs to two megacolumns, according to Ushio.

With all its tribulations, steel
erection constrained the pace of the following team, charged
with pumping concrete from the ground to a record-breaking
455 m, says Akira Inoue, KTRTs engineering manager.
To avoid interfering with the steel erectors, crews filled
each tier of megacolums from the bottom up.

Installing the curtain wall, which
consists of 17,000 low-emissivity, double-glazed panels within
marine-grade aluminum frames, followed the concrete and is
set to be done this month.

"At one point we were installing
120 panels...almost one floor a day," says Stuart Orr,
general manager of Josef Gartner & Co. (HK) Ltd., Gundelfingen,
Germany. The firm picked up the pieces with an $84-million
contract early in 2001 after the original installer left because
of financial problems, says MacKay.

"We were taking on something
we hadnt started and we didnt have time to understand
what was happening," says Orr. "All the different
components in different stages of completion were handed over
to us. We had to pick this up from raw material in the factory
and all the way through the process."

The trials have boosted the construction
cost by some $60 million. But the price is still within contingencies,
estimates Lin. Adds MacKay: "We are striving very hard
to maintain the budget."

The Virginia Dept. of Transportation
stopped construction for five days on a $650-million interchange
project in Springfield after two construction workers died
there in two weeks. A third worker died on the job last October.

Giant Damper
Doubles as Buildings Interior Adornment By Peter Reina

Taipei 101s
megacolumns will ensure the towers survival in
earthquakes and typhoons, but in times of relative calm
a 6-meter-dia steel ball will ensure user comfort.

The 660-tonne tuned mass
damper and its support occupy five upper floors. The
damper is visible from a mezzanine level and is probably
the largest of its kind and the first to form part of
a buildings architecture, claim the designers.

Motioneering Inc.,
Guelph, Ontario, has a $3.5-million turnkey contract
for dampers in the tower and its 60-m-tall pinnacle.
The contract excludes the roughly $800,000 damper ball
itself, which was supplied and installed by the towers
steel subcontractor. Click
here to view diagrams

Towers
tuned mass damper was assembled on site from 12-cm-thick
steel plate.

Assembled on site in layers
of 12.5-cm-thick steel plate, the damper ball is welded
to a steel cradle suspended from level 92 by four sets
of cables. Eight primary hydraulic pistons, each about
2 m long, grip the cradle to dissipate dynamic energy
as heat, explains Jamieson Robinson, Motioneerings
project manager.

The damper will reduce the
towers peak vibrations by more than one- third,
say Motioneering officials. But the damper will not
have any role during earthquakes. Then, the main concern
is to ensure that the steel ball stays in control and
does not swing wildly and destructively.

A roughly 60-cm-dia pin projecting
from the underside of the ball limits its movement to
about 1 m. The pin is constrained by a steel ring attached
to hydraulic pistons anchored between floors 87 and
88. During seismic or wind events with 100-year return
periods, the pin "nudges" the ring and energy
is dissipated through pistons, says Robinson.

For the 60-m-tall pinnacle
rising from the 101st floor, the main worry is structural
fatigue from vortex-induced oscillations under common
wind conditions, says Motioneering. Two 7-tonne dampers
will control the oscillations. These dampers are flat
steel masses tuned by springs and are able to move horizontally
in any direction.

Because clearance inside
the pinnacle is under 1.5 sq m, the springs are loaded
vertically below the mass, says Robinson. Cables connect
each mass to the springs.

To prevent damage during
earthquakes, pinnacle dampers have a locking device
that will be automatically triggered. It will prevent
the dampers and pinnacle from moving independently.

When structural work ends
later this month, Motioneering will fine-tune the dampers.
The team will then return periodically over the next
two years to monitor the devices, though Robinson hopes
to have access beyond that. "We like to be involved
with long-term maintenance programs for all of our installations,"
he says.